1. Field of the Invention
This invention relates to a fluid circuit, and more particularly to a fluid circuit including an actuator, in which the pressure of a fluid for effecting a return stroke of a piston in the actuator is regulated for the purpose of saving required for the return stroke of the piston.
2. Description of the Prior Art
It has been a common practice to apply a fluid pressure to a cylinder of an actuator to displace a piston, so that the movement of a piston rod connected to the piston may be taken out as a work. In this respect, a work carried out by the actuator depends on a fluid pressure acting on the side of a piston in a piston-head-side chamber. On the other hand, a pressure required for a return stroke of a piston (a pressure acting on the side of a piston in a piston-rod-side chamber) should not necessarily be as high as that required for the advancing stroke of a piston and thus may be reduced to the possible lowest level. Conventionally, however, it has been a practice that after the pressure regulation, a fluid pressure of the same level is applied to a piston-head side chamber as well as to a piston-rod side chamber, with the direction of a pressure fluid being switched by means of a flow-direction change-over valve. In other words, an excessive fluid pressure is used for the return stroke of a piston in the actuator.
Meanwhile, the speed control of a piston reciprocating within a cylinder of an actuator is classified into two types, i.e., a meter-out control type and a meter-in control type. In meter-out control type, when checking an actuator after completion of a work, a pressure within a cylinder of the actuator remains at an atmospheric pressure, so that the speed control of a piston is only possible when a pressure is being applied. Thus, in the other cases, the speed control of a piston becomes impossible, so that there often takes place a damage of a fixture or an accident of an operator. For this reason, an operator should pay excessive attension at the beginning of a work, thus lowering an operational efficiency. Accordingly, the meter-in control finds a wide application in this phase of industry. However, the meter-in control type suffers from disadvantages in that a pressure build-up time in a cylinder depends on the flow rate of a fluid being fed into the cylinder, and hence there results a slow return stroke of a piston which leads to a lowered operational efficiency.